DESCRIPTION: This application will examine gravity's role in equilibrium development by raising fish in an earth-bound apparatus that simulates a microgravity environment. This NASA-developed apparatus, the Rotating Wall Perfused Vessel (RWPV), creates a microgravity-like environment by using rotational vectors to balance out the pull of gravity. The investigator has adapted this device to culture zebrafish eggs and has successfully hatched and raised zebrafish in the vessel. Preliminary data show clear behavioral and morphological effects in most subjects raised in this environment, including deficits in normal equilibrium orientation, compensatory eye movements, and otolith development. Four sets of experiments are proposed for comparison of microgravity-raised fish and normal fish; subjects will be examined for differences in orientation behavior, eye movement, receptor morphology and primary afferent projections. Two fish species will be examined: zebrafish, which are a well-accepted model for CNS development, and medaka, which have already been successfully hatched and reared during Space Shuttle flights. Fo the later receptor morphology and projection studies, Space Shuttle-reared zebrafish are expected to be available for comparison with subjects raised in the earth-based microgravity simulator.